The present invention relates to a new and improved construction of a cooling apparatus for cooling an object.
In its more particular aspects the present invention specifically relates to a new and improved construction of a cooling apparatus for cooling an object and which cooling apparatus contains a first cooler having an expansion or depressurization outlet. A pressurized first gas which is procooled below its inversion temperature, is passed through the expansion or depressurization outlet and is thereby depressurized with cooling. The cooling apparatus further contains a second cooler which is operated using a second gas for precooling the first gas.
For the purpose of clarification and definition of terms in the instant applications, the following is specifically noted: An expansion cooler is understood to define a cooler which operates by expanding or depressurizing a precooled pressurized gas in order to utilize the Joule-Thomson effect for further cooling down the gas. This gas is, then, employed for cooling an object. A Joule-Thomson cooler is understood to likewise define a cooler which operates by expanding or depressurizing a precooled pressurized gas for further cooling down the gas. This gas is, then, returned and passed through a return flow path of a heat exchanger for precooling the pressurized gas passing through a forward flow path of such heat exchanger.
In a cooling apparatus such as known, for example, from British Patent No. 1,238,911, cooling of a pressurized gas is achieved by expansion or depressurization effected by passing the gas through a nozzle. For this purpose, the gas must have a temperature below its inversion temperature prior to expansion or depressurization. The cooling apparatus according to British Patent No. 1,238,911 is provided with two coolers. In a first one of the two coolers a first gas is conducted in the gaseous state from a source of pressurized gas along a first path of a countercurrent heat exchanger, expansion or depressurized by passage through the nozzle and returned along a second path of the heat exchanger in counter-current fashion. As a result, the forward flowing pressurized gas is cooled. A second one of the two coolers causes the first to be precooled prior to arrival at the countercurrent heat exchanger of the first cooler. In this arrangement, a pressurized liquid is fed to the second cooler and sprayed into a chamber through a nozzle. During this operation, the liquid evaporates whereby the cooling action of the second cooler is achieved. The first cooler in this arrangement cools an object in the form of an infrared detector.
In German Published Patent Application No. 3,642,683, published Jun. 16, 1988, which is cognate with U.S. Pat. No. 4,819,451, granted Apr. 11, 1989, there is described a cryostat which is based on the Joule-Thomson effect and serves for cooling an infrared detector. A countercurrent heat exchanger including a forward flow line or conduit, is located in a Dewar vessel. The forward flow line or conduit terminates in an expansion or depressurization nozzle. The infrared detector is located at an end wall of the inner side of the Dewar vessel. A heat insulating layer is disposed between a base and the Dewar vessel for reducing the heat load. An inlet end of forward flow the line or conduit is cooled by Peltier elements in order to improve upon the cooling power achievable by such Joule-Thomson process at a given mass flow of pressurized gas.
German Published Patent Application No. 1,501,715, published on Oct. 30, 1969, relates to gas liquefying apparatus containing two expansion coolers operated by respectively using hydrogen and air or nitrogen. Both of the expansion coolers are constructed in the manner of Joule-Thomson coolers, i.e. contain respective countercurrent heat exchangers in which the respective expanded or depressurized and cooled gas is subject to heat exchange with the forward flowing gas. The liquid nitrogen or air obtained by a second one of the two Joule-Thomson coolers serves for precooling hydrogen in the first one of the two Joule-Thomson coolers. The hydrogen is thereby cooled down below its inversion temperature. However, nitrogen can be cooled by the respective Joule-Thomson cooler only down to its boiling point.
A similar arrangement is shown in German Published Patent Application No. 1,501,106, published on Jan. 8, 1970.
European Published Patent Application No. 0,271,989,published on Jun. 22, 1988, describes a conventional single-stage Joule-Thomson cooler using a coolant in the form of a mixture of nitrogen, argon and neon and methane, ethane or propane with the addition of a combustion inhibiting material like bromotrifluoromethane.
German Published Patent Applications No. 3,337,194 and 3,337,195, both published on Apr. 25, 1985, British Published Patent Application No. 2,119,071, published on Nov. 9, 1983, and European Published Patent Application No. 0,234,644 are all concerned with the use of a single-stage Joule-Thomson cooler for cooling electronic or opto-electronic components.
In copending U.S. patent application Ser. No. 07/563,433, filed on Aug. 7, 1990, there is proposed for gyro-stabilized seekers containing a planar image resolving detector, arranging the seeker on a support. The support is aligned to the gyro rotor and thus to the optical axis of the imaging optical system so that the plane of the planar detector is constantly oriented perpendicular to this optical axis even in the event of seeker "squint". In this arrangement there exists the problem of detector cooling. When using conventional Joule-Thomson coolers for cooling such detectors, there is provided a countercurrent heat exchanger through which expanded or depressurized and cooled gas is returned for precooling the incoming gas flow. During this operation, the expanded or depressurized gas should be utilized as completely as possible for the precooling process and gas losses as well as heat losses must be avoided. This can be achieved if the detector is stationarily arranged in a Dewar vessel. Difficulties result, however, when the detector is arranged at a movable support.